The present invention relates generally to integrated circuit interfaces, and more specifically to integrated circuit interfaces having current mode drivers.
Integrated circuits typically have dedicated interface circuits to communicate with other integrated circuits and other systems. Signals that travel from one integrated circuit to another are becoming faster and faster. As signal speeds increase, the effect of imperfect xe2x80x9cchannelsxe2x80x9d also increases. A xe2x80x9cchannel,xe2x80x9d for the purposes of this description, is any medium that the signal passes through. For example, a channel may consist of printed circuit board traces or wires routed between integrated circuits. One possible effect of an imperfect channel is frequency dependent attenuation of signal amplitudes. In general, when the signal amplitude is attenuated as a function of frequency, the signal becomes smaller as the speed increases. When the signal gets too small, communications between integrated circuits can become unreliable.
One known method for compensating for frequency dependent attenuation is the use of pre-equalization at the driver. Pre-equalization adjusts the amplitude of the driver depending on the frequency of outbound data. Successful pre-equalization compensates for signal loss in the channel, and results in a substantially constant amplitude received voltage wave for low and high frequency data. One mechanism for pre-equalization is described in: Ramin Farjad-Rad, Chih-Kong Ken Yang, Mark A. Horowitz, and Thomas H. Lee, xe2x80x9cA 0.4-um CMOS 10-Gb/s 4-PAM Pre-Emphasis Serial Link Transmitter,xe2x80x9d Vol. 34, No. 5, IEEE Journal of Solid-State Circuits, (May 1999).
In addition to problems associated with increased signal speed, modem integrated circuits suffer from too many external interconnects. As more circuitry is placed in integrated circuits, the need for additional xe2x80x9cpinsxe2x80x9d on the integrated circuits has increased dramatically.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternate integrated circuit interfaces.